The present invention relates to electrical switchgear, and more particularly, to an adapter system and method for retrofitting existing switchgear with new, removable circuit breakers.
Many types of low- and medium-voltage switchgear systems use circuit breakers that can be withdrawn for maintenance. Typically, such a circuit breaker is moved into and out of a switchgear cell by a racking mechanism having arms disposed on opposing sides of the circuit breakers and which are only movable simultaneously. Further, such a circuit breaker typically has an interlock that prevents the circuit breaker from being moved into or out of connection with the bus bar in the switchgear cell when the circuit breaker is closed.
As a switchgear installation ages, the old circuit breakers mounted therein often need to be replaced. Many times, the manufacturer of the switchgear installation is out of business when replacement is required. Since circuit breakers from different manufacturers are typically not interchangeable, old circuit breakers from defunct manufactures typically cannot be directly replaced by new circuit breakers from current manufacturers. Even for a particular manufacturer, new circuit breakers are typically different in size and operation than old circuit breakers and typically cannot directly replace the old circuit breakers. Thus, the owner of an old switchgear installation who needs to replace old circuit breakers is typically presented with a limited number of options. The owner can replace the entire switchgear installation, extensively modify the new circuit breakers, or extensively modify the switchgear cells, all of which are quite expensive. In some cases, the owner may be able to use adapters or “cradles” to adapt new circuit breakers for use in existing switchgear cells. This latter technique is often referred to as a “cradle-within-a-cradle” technique.
In a “cradle-within-a-cradle” technique, a new circuit breaker is inserted into a cradle which is then removably mounted inside an existing switchgear cell. The cradle moves in and out of the switchgear cell and connects to the switchgear bus bar in substantially the same manner as the old circuit breaker that was previously mounted inside the switchgear cell. Conventionally, the cradle translates the operation of the racking mechanism of the new circuit breaker into a racking operation that is substantially similar to the racking operation of the old circuit breaker and connects the terminals of the new circuit breaker to terminals that are substantially the same as the terminals of the old circuit breaker. A conventional cradle is often complex and does not have an interlock that prevents the cradle from being moved into or out of a switchgear cell when it is carrying a closed circuit breaker.
Based on the foregoing, there is a need for a less complex cradle with an interlock and a method of using the same. The present invention is directed to such a cradle and method.